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      <title>4、LinkedHashMap 的实现 - 交互式测验</title>
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          <div class="quiz-container">
            <div class="quiz-header">
              <h1>4、LinkedHashMap 的实现 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
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      <script>
        const quizData = [
  {
    "question": "LinkedHashMap在HashMap的基础上增加了什么核心特性？",
    "options": [
      "实现了线程安全，适用于高并发场景。",
      "通过内部维护一个双向链表来保持元素的顺序。",
      "使用红黑树优化哈希冲突，提高了查询性能。",
      "只允许null作为一个键。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "LinkedHashMap的核心优势在于它继承了HashMap的快速查找能力（平均O(1)复杂度），同时通过一个内嵌的双向链表维护了元素的插入顺序或访问顺序。这使得遍历LinkedHashMap时可以得到一个可预测的、有序的结果。",
    "source": "文档中「内部结构」部分",
    "hint": "文档提到它既有HashMap的特性，又有LinkedList的特性，思考一下它是如何结合两者的。"
  },
  {
    "question": "在LinkedHashMap中，构造函数的`accessOrder`参数设置为`true`时，会产生什么效果？",
    "options": [
      "元素将按照它们被插入的顺序进行迭代，且访问操作不影响顺序。",
      "在插入新元素时，会自动根据键的大小进行排序。",
      "每当通过`get`方法访问一个元素时，该元素会被移动到链表的末尾。",
      "元素将严格按照其哈希值的顺序进行排序。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "当`accessOrder`为`true`时，LinkedHashMap会切换到“访问顺序”模式。在这种模式下，任何对已有条目的`get`操作都会将该条目从其当前位置移动到双向链表的尾部，这使其成为实现LRU（最近最少使用）缓存的理想选择。",
    "source": "文档中「查询操作」部分",
    "hint": "文档中提到，这个特性是实现LRU缓存的关键。思考一下LRU缓存是如何工作的。"
  },
  {
    "question": "根据文档，使用`LinkedHashMap`实现一个简单的LRU（最近最少使用）缓存，除了在构造时将`accessOrder`设为`true`外，还需要重写哪个方法来定义淘汰策略？",
    "options": [
      "removeEldestEntry(Map.Entry<K, V> eldest)",
      "afterNodeInsertion(boolean evict)",
      "put(K key, V value)",
      "getNode(int hash, Object key)"
    ],
    "correctAnswerIndex": 0,
    "explanation": "为了实现LRU缓存的淘汰策略，需要重写`removeEldestEntry`方法。每当有新元素插入时，LinkedHashMap会调用此方法，并传入链表头部的“最老”的元素。如果此方法返回`true`，该最老的元素就会被移除。开发者可以在此方法中定义自己的淘汰逻辑，例如当`size()`超过预设容量时返回`true`。",
    "source": "文档中「元素插入」部分",
    "hint": "文档中的商品缓存代码示例里，判断是否“超过容量就移除最久未使用的”逻辑是在哪个方法中实现的？"
  },
  {
    "question": "文档提出了一个观点：在某些场景下，全量遍历`LinkedHashMap`可能比遍历`HashMap`更快。这是为什么？",
    "options": [
      "因为`LinkedHashMap`的内部数组大小总是恰好等于元素数量，没有空间浪费。",
      "因为`LinkedHashMap`在遍历前会对所有元素进行一次快速排序。",
      "因为`LinkedHashMap`的迭代器沿着连续的双向链表进行，对CPU缓存更友好，且无需跳过空的哈希桶。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "HashMap的迭代需要遍历其内部的哈希桶数组，这其中可能包含大量未使用的`null`桶，并且元素在数组中的分布是无序的，对CPU缓存不友好。相比之下，`LinkedHashMap`的迭代器直接从链表的`head`节点开始，沿着`after`指针顺序遍历所有元素，访问是连续的，效率更高。",
    "source": "文档中「迭代性能」部分",
    "hint": "思考一下HashMap和LinkedHashMap在内存中存储元素的方式有何不同，以及这如何影响遍历过程。"
  },
  {
    "question": "相比于`HashMap`，文档指出了`LinkedHashMap`存在哪些性能上的代价？",
    "options": [
      "查询（get）操作的平均时间复杂度从O(1)劣化到O(log n)。",
      "内存占用更大，且插入和删除操作因为需要维护链表而稍慢。",
      "在数据量大时，更容易发生哈希冲突。",
      "不支持null键和null值。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "为了维护有序性，`LinkedHashMap`的每个`Entry`节点都比`HashMap`的`Node`多了两个引用（`before`和`after`），这导致了更大的内存开销。同时，在进行插入和删除操作时，除了要处理哈希表，还必须维护双向链表的指针，这会带来额外的性能开销。",
    "source": "文档中「性能考量」部分",
    "hint": "文档中提到“凡事有利有弊”，为了获得“有序性”这个好处，LinkedHashMap付出了什么代价？"
  },
  {
    "question": "在“案例2：保持API响应顺序一致”中，作者是如何利用`LinkedHashMap`解决金融机构API要求的字段顺序问题的？",
    "options": [
      "通过重写`removeEldestEntry`方法，过滤掉不符合顺序要求的字段。",
      "利用`LinkedHashMap`默认的插入顺序特性，确保在构建响应JSON时，字段的顺序与请求参数的顺序一致。",
      "通过将`accessOrder`设置为`true`，使得最常被访问的字段排在前面。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "该案例利用了`LinkedHashMap`的默认模式——插入顺序模式（即`accessOrder`为`false`）。当按顺序将键值对放入`LinkedHashMap`后，遍历它时，元素的顺序会和放入时的顺序完全一样。这巧妙地解决了API要求响应字段顺序与请求字段顺序保持一致的问题。",
    "source": "文档中「案例2：保持API响应顺序一致」部分",
    "hint": "该案例利用了`LinkedHashMap`的哪种默认的行为模式，是插入顺序还是访问顺序？"
  },
  {
    "question": "`LinkedHashMap`的内部静态类`Entry`是如何同时支持哈希表功能和链表功能的？",
    "options": [
      "它内部包含一个`HashMap.Node`对象和一个独立的`LinkedListNode`对象。",
      "它通过一个时间戳字段来记录元素的插入或访问时间。",
      "它重写了`hashCode()`和`equals()`方法以实现有序存储。",
      "它继承了`HashMap.Node`来处理哈希相关功能，并额外增加了`before`和`after`两个引用来构建双向链表。"
    ],
    "correctAnswerIndex": 3,
    "explanation": "文档中的源码片段显示，`static class Entry<K,V> extends HashMap.Node<K,V>`。这表明`Entry`通过继承获得了`HashMap.Node`的所有属性（如`hash`, `key`, `value`, `next`），从而能参与到哈希表的运作中。同时，`Entry`类自己定义了`Entry<K,V> before, after;` 这两个指针，用于将所有节点串成一个双向链表，以维护顺序。",
    "source": "文档中「内部结构」部分",
    "hint": "查看文档中`Entry`类的定义，它与其他类有什么关系，又自己增加了哪些成员变量？"
  }
];
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            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

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                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
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                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
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                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  